1. Field of the Invention
The present invention relates to an optical transmitter module.
2. Description of the Related Art
As a modulation method for an optical signal for use in optical communication, there has been known a pulse amplitude modulation (PAM) for encoding a signal, utilizing a difference in optical amplitude. The PAM is roughly classified into direct modulation for modulating optical amplitude of a semiconductor laser and external modulation for modulating a laser beam from a semiconductor laser, using an optical modulator. As an optical modulator for external modulation, an electro-absorption optical modulator (hereinafter referred to as an EA modulator) may be used.
JP 2015-207803 A discloses a digital/analog converter circuit for converting a digital input of two bits or greater into an analog output at four or greater levels.
JP 2001-159748 A discloses a semiconductor optical function device having optical modulators connected in series or in parallel.